1. Field of the Invention
The present invention relates to an apparatus for converting a sound signal into vibration so as to stimulate the human hearing organs through the bones. More particularly, it has adopted an iron core and an inertial mass in order to achieve high power output.
2. Related Prior Art
Conventionally, a bone-conducting loudspeaker has been developed for persons who have difficulty hearing. This loudspeaker is a kind of acoustic transducer that enables an auditorily handicapped person who does not have the tympanic membrane to hear by stimulating the auditory nerves through the cranial bone instead of the tympanic membrane. Basically, the bone-conducting loudspeaker produces sound through the medium of liquid or solid matter, such as the human body, while the conventional loudspeaker uses the atmosphere.
FIG. 1 is a structural diagram roughly showing the conventional acoustic loudspeaker. As shown, a permanent magnet 3 is fixed to a conical frame 1. One pole of the magnet 3 is inserted in a cylindrical electromagnet 7 around which a voice coil 5 is wound and which has a closed face. To the closed face of the electromagnet 7, a conical vibrating diagram 9 is attached. This diaphragm 9 vibrates back and forth (in the direction of Y in FIG. 1) along with the electromagnet 7. More specifically speaking, when an acoustic signal V is applied to the voice coil 5, the coil 5 produces magnetic force. The magnetic force interacts with the magnet 3 to move the electromagnet 7. Thereby the diaphragm 9 vibrates and regenerates acoustic sound by generating pressure waves in the surrounding atmosphere.
Meanwhile, in order to expand the functionality of hearing aids for auditorily handicapped persons, a “body-sensible loudspeaker” has been developed, by which a user can sense the acoustic energy generated from an audio system through the tactile organs rather than the auditory organs. The body-sensible loudspeaker, which converts the acoustic signal into vibration to stimulate the human body, provides even more vivid sound in comparison with the conventional acoustic loudspeaker. It can be used for vehicle seats, game devices, theatre seats, etc.
However, in the conventional body-sensible loudspeaker, high power output cannot be obtained because it directly uses the same structure as the conventional acoustic loudspeaker (see FIG. 1). In the conventional acoustic loudspeaker, the vibrating diaphragm is made of a soft material, such as paper or PVC. Thus, it has a disadvantage that:
The service life of the coil is limited by the heat generated by the electric current, which must be increased when the output power is made higher. Moreover, if the fundamental oscillation frequency of the vibrating diaphragm coincides with the frequency of the amplified acoustic signal, the diaphragm may resonate. This will cause the diaphragm to abnormally oscillate, blocking the response over a certain frequency range.